Satellite Positioning System antennas and receivers, such as those for the Global Positioning System (GPS) and for the Global Orbiting Navigational System (GLONASS) discussed below, are now used for many applications requiring determination of the observer's location anywhere on or in the vicinity of the Earth.
A differential GPS (DGPS) receiver includes a GPS antenna to receive the GPS signals transmitted from one or more GPS satellites, a GPS processor to calculate the GPS antenna's position mid time of observation of that position from the GPS signals, a display processor to convert the GPS position and observation time into information that is useful for an application, and a display to present the information to the user, and a DGPS antenna and processor to receive and apply differential corrections to produce GPS signals with improved accuracy. The GPS antenna must be positioned with a direct line of sight to the GPS satellite or satellites from which the receiver receives GPS signals.
Current GPS receivers adopt one of two formats. The first format, commonly called "handheld," includes a GPS antenna, a GPS processor, a display processor, and a display in a single unit. A DGPS antenna and receiver are provided in a separate unit or units that is connected to the GPS processor. A problem with this format is that the user must remain in the open to preserve a direct line of sight from the GPS antenna to one or more GPS satellite while operating and observing the user's display.
The second format places the GPS antenna in an antenna unit and the display in a separate display unit. The GPS processor and the display processor may be contained in the antenna unit, in the display unit, or in a separate unit or units. This format allows the user to separate the GPS antenna and the display so that the GPS position and time information can be observed and operated upon in a protected environment. A DGPS antenna and receiver are provided in a separate unit or units connected to the GPS processor in this format also.
In either format, a cable is used to connect the GPS processor to the DGPS antenna and receiver, to the GPS antenna unit, to the display unit, and/or to any unit(s) that depend upon the GPS processor. This requires that the DGPS antenna and receiver and any cable(s) connecting these units to the GPS receiver be moved together with the GPS receiver as an observer moves around within a region. These connections are often bulky, expensive and prone to breakage or malfunction.
Workers in other technical areas have developed some related technology. Westerfield, in U.S. Pat. No. 4,622,557, discloses a transdigitizer for relaying signals received by a buoy from GPS satellites to an aircraft containing a GPS processing station that is spaced apart from the buoy. The buoy receives GPS satellite signals, downconverts the signals frequencies, and transmits the GPS signals to the aircraft, where the location of the buoy is determined with a certain inaccuracy. The buoy is quite large as it must float on the water's surface, and no GPS processing is performed on or adjacent to the buoy.
U.S. Pat. No. 4,641,366, issued to Yokoyama et al, discloses use of portable radio (handset) apparatus, including first and second antennas recessed into one side of the portable radio and capable of receiving signals in two separate frequency bands to which the radio responds. The radio apparatus includes one or two frequency converters to convert between audio and rf frequencies.
A small, handheld antenna is disclosed in U.S. Pat. No. 4,701,763, issued to Yamamoto et al. FIG. 14 of this patent illustrates application of this antenna concept to an rf signal receiver or transmitter. The high gain antenna is small enough to be insertable into many types of signal-receiving electronics devices, such as pagers. Most of this disclosure is concerned with the three-layer structure of the antenna.
Fowler, in U.S. Pat. No. 4,754,283, discloses a cordless GPS sounding device using two antennas, a first antenna to receive radiowaves from an antenna carried by a balloon aloft that indicates wind direction and velocity, and a second antenna to receive conventional GPS signals from a GPS satellite. The ground-based GPS signal receiver and antenna are connected by cables or wires to the balloon-sensing antenna and to a computer for determining wind direction and velocity as the balloon drifts relative to the ground-based receiver.
Blaese discloses a portable antenna suitable for mounting on a motor vehicle's side window, in U.S. Pat. No. 4,804,969. The mounting means facilitates easy installation and removal. The antenna apparatus includes a pivotable or fold-out, current feed line radiator, which is mounted on the outside surface of the window and is electrically attached to other portions of the antenna electronics located on the inside surface of the window. A coaxial cable connects the inside surface electronics to a separate transceiver located inside the vehicle. The line radiator includes a 5/8 wavelength radiator, stacked on a helical separation coil, stacked on a 3/8 wavelength radiator, for field cancellation purposes. Blaese discloses a cordless, easy-mount antenna of similar design that obviates the need for the coaxial cable, in U.S. Pat. No. 5,059,971; a second line radiator provides a wireless link with the transceiver.
A very thin radio housing having a printed circuit loop antenna mounted in a plane on an interior wall of the housing is disclosed by Urbish et al in U.S. Pat. No. 4,894,663. The housing opens as a notebook would open, to disclose the antenna and a portion of the antenna electronics, and a portion of the antenna circuit is located on a hinge that facilitates opening and closing the housing. The antenna, electronics and housing are intended to serve as a credit card size page signal receiver or other signal receiving system.
Newland discloses a small antenna for a cordless telephone in U.S. Pat. No. 4,897,863. The tip-and-ring wiring in the associated telephone handset serves as the antenna, which provides telecommunication capability with the rest of the world through a wireless link to inside telephone wiring in an adjacent structure, such as a home. The tip-and-ring wiring thus serves as both a signal feed line and as an antenna. Audio and radio frequency signals can be transmitted and received using this antenna.
Mori et al, in U.S. Pat. No. 4,935,745, disclose a credit card size radio receiver with a slot antenna integrated as part of the receiver housing. Three contiguous sides of the card size housing together serve as the antenna. An rf frequency circuit (not shown) receives and processes the incoming radio signals and is carried by the housing. The apparatus is intended to serve as a card size page signal receiver.
U.S. Pat. No. 5,052,645, issued to Hixon, discloses a telescoping pole antenna that can be used to support a GPS signal antenna. The pole includes many concentric telescoping, vertically oriented cylinders that can be collapsed to one meter in height or extended to a height of as much as 20 meters. The antenna and telescoping support pole combination is not portable and would probably have a mass of several tens of kilograms.
A credit card size radio page signal receiver, with a portion of the receiver housing serving as an antenna, is disclosed in U.S. Pat. No. 5,054,120, issued to Ushiyama et al. Top and bottom walls of the housing serve as part of a loop antenna that can handle VHF signals. The antenna is not defined by any particular circuit integrated with the housing.
Raubenheimer et al disclose a handheld navigational aid, including a keyboard for data entry, a visual display and a loudspeaker for audible communication, in U.S. Pat. No. 5,059,970. The visual display presents a small map of a chosen region, and the map provides two cursors to indicate and determine the distance between two points on the map. An icon indicates the position of a chosen marine or airborne vessel on the map, and present position relative to a fixed reference point is visually displayed as distance/bearing or as latitude/longitude coordinates in a two-dimensional representation. The apparatus contains a microprocessor and stored-on-board algorithms and mathematical equations for signal processing purposes and relies upon a resettable internal clock for certain display purposes. Input signals appear to be entered through the keyboard.
A coupler that avoids use of a hardware connection between a stationary remote GPS signal antenna and a handheld GPS receiver with a display window is disclosed by Mason et al in U.S. Pat. No. 5,239,669. The coupler is connected to, and receives GPS signals from, the remote antenna by an interconnect cable. The coupler includes a driver circuit and an antenna that receives and transmits the GPS signals to the handheld GPS receiver, which must be within six feet of the coupler.
What is needed is Differential Global Positioning System (DGPS) apparatus, contained in a single antenna;like package, that: allows the user to place a GPS antenna in a direct line of Sight from one or more GPS satellites; allows the user to operate and observe the position and/or observation time display in-a protected environment; and allows receipt and processing of differential GPS radiowave signals to determine the corrected location and/or observation time for the device using GPS methods. Preferably, the system should allow the user and display unit to move around without the inconvenience and poor reliability associated with use of a cable or cord.